Overtone spectroscopy of methyl C-H stretch vibration in CH3CF2Cl and CH3CFCl2

Photoacoustic spectra of the second (3 nu(CH)), third (4 nu(CH)), and fourt h (5 nu(CH)) overtones of the methyl C-H stretches in CH3CF2Cl and CH3CFCl2 were measured. The spectra are characterized by a multiple peak structure of partially resolved triplets and quartets with an anomalous linewidth dec rease in the 4 nu(CH) region. The results are interpreted in terms of a sim plified local mode model for C-H stretching vibrations, including also the stretch-deformation Fermi resonances. The model accounts for most spectral features and allows determination of the time scale for vibrational redistr ibution. (C) 2000 American Institute of Physics. [S0021-9606(00)01008-4].